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JOINE OF AGEIOITIAL RESEARCH 

DEPARTMENT OF AGRICULTURE 



Vol. IV Washington, D. C, Mav 15, 1915 No. 2 



SEEDLING DISEASES OF SUGAR BEETS AJS^D THEIR 
RELATION TO ROOT-ROT AND CROWN-ROl' 

By Hi A. Edson 

I . ' ' ^ WISCONSIN 



PH. i), TliESiS jLOi^ 



s^ 



^'^$^- 



TO 



136 Journal of Agricultural Research voi. iv. No. 3 

serious losses. Many of the failures attributed to faulty germination are, 
in fact, the results of serious outbreaks of this disease, and in practically 
all the cases investigated where seedlings were "not growing well" the 
trouble has been found to be root sickness. 

These or similar diseases have been known for a long time in Europe, 
where various and widely different theories have been advanced regarding 
their cause or causes. Refractory soil, cold ground, wet weather, poor 
cultivation, excessive rain, fungus infection, and the like have all had 
their advocates, who have based their opinions in many instances upon 
insufficient data. 

Hesse (24) ' reported the presence of Pythium debaryanum in diseased 
beet seedlings in 1874, but he seems to have done no experimental work 
with this host. Hellriegel (23), one of the first investigators who made 
a careful experimental study of this subject, showed that damping-o£f 
in his pot experiments appeared to be due to a parasite, and traced the 
source of infection to the seed. He did not, however, assign a specific 
organism as the cause. Eidam (13) produced artificial infection of beet 
seedlings with cultures of Rhizoctonia betae Kiihn. Kriiger (25, 26) 
found Phoma betae Fr. to be an active seedling parasite of the sugar beet 
and expressed the opinion that Several different fungi are capable of pro- 
ducing diseases in seedlings of this plant so similar in appearance that 
they have been classed together under the name " Wurzelbrand." Sev- 
eral fungi, as well as bacteria, have since been added to this list of para- 
sites, while other writers have denied the parasitic origin of the disease. 

So much contradiction and uncertainty exists in the literature of the 
last 20 years regarding the nature and cause of Wurzelbrand of beets 
in Europe that Peters (31, 32, 33) and his associates (5, 6) found it neces- 
sary to go over the entire subject and submit to rigid experimental proofs 
the more worthy of the hypotheses that have been put forth. 

From what appears to be a careful and trustworthy piece of work, 
Peters (33) concludes that under the conditions of his experiments 
Pythium debaryanum Hesse, Phoma betae Fr., and Aphanomyces laevis 
De By. are capable of producing damping-off of the sugar beet. He was 
unable to secure pure cultures of Rhizoctonia molacea Tul., but he infected 
soil with fragments of beets showing typical Rhizoctonia decay and 
failed to produce damping-off. The evidence of the parasitism of bac- 
teria on this host seemed to him insufficient to justify serious consideration. 

In America the only reported work on seedling diseases of beets, 
except the author's preliminary note (12), is by Duggar (9, 11), who 
conducted successful infection experiments with a species of Rhizoc- 
tonia that he secured from decayed beets and later designated as Cor- 
ticium vagum, B. and C, var. solani Burt. (10, p. 444—452). His experi- 
ments were carried out in sterilized soil and controlled by check plants 

1 Reference is made by number to " Literature cited," p. 165-168. 



D. of d; 

MAY U f9I6 



Mayis. I9I5 ScedUng DiseasBS of Sugar Bects 137 

which remained healthy, but he makes no mention of treating the seed 

to insure the elimination of Phoma betae, which he regarded as absent 

(10, p. 344). 

THE SECURING OF CULTURES 

The first steps in the present work were naturally the securing of cul- 
tures, which were obtained in various ways. Beet seed was placed in 
sterilized filter papers in sterile moist chambers, and transfers were made 
from the colonies of fungi which developed during the progress of ger- 
mination. This method is uncertain and yields a large number of 
harmless saprophytes. Seed was sown in soil which had been sterilized 
in an autoclave at 12 pounds' pressure for from four to six hours on two 
successive days. These were watered with sterile water and protected 
from outside sources of infection. Whenever damping-off appeared, 
the diseased seedlings were removed and treated for one minute with 
more or less shaking in a solution (1:1 ,000) of bichlorid of mercury in water 
or in similar bichlorid solutions containing either i gm. of ammonium 
chlorid or ^ c. c. of concentrated hydrochloric acid per liter. They 
were then rinsed in sterilized water and dropped upon suitable nutrient- 
agar medium in Petri dishes (PI. XVI and XVII). The agar most 
commonly used is sufficiently acid to materially check the development of 
bacteria and is at the same time a very satisfactory medium for the 
cultivation of most fungi. It has the following composition: 

Dextrose 100 Dipotassium hydrogen 

Peptone 5 phosphate 2. 5 

Ammonium nitrate 10 Calcium chlorid .1 

Potassium nitrate 5 Water i, 000 

Magnesium sulphate. ... 2. 5 Agar 20 

As soon as growth appeared from the seedlings, isolation transfers were 
made. Cultures obtained by these two methods were regarded as origi- 
nating from the seed. 

Cultures were made from the soil indirectly by means of seedlings in 
the following manner: Beet seed, treated by a method to be discussed 
later, so as to insure the absence of parasitic fungi, was sown in unster- 
ilized soil in pots that were thoroughly sterilized before using. When 
damping-off occurred, isolations were made in the manner already 
described. Cultures were secured from decayed beets by cutting out 
with a sterile knife small portions of material on the border line between 
healthy and diseased tissue. These blocks were placed upon a suitable 
medium, and isolations were made from the developing colonies. Another 
method employed was to sow treated beet seed in sterilized soil, subse- 
quently infected with fragments of decaying beets. Isolations were then 
made from the seedlings when disease developed. Large numbers of 
isolations were made from sugar-beet seedlings grown in commercial 
fields, and a considerable number of cultures were courteously contrib- 
uted by various workers from time to time. 



138 Journal of Agricultural Research voi. iv, No. 3 

SEED TREATMENT 

Sugar-beet seed is quite universally infected with parasitic fungi. It 
was therefore necessary to devise some method of freeing the seed from 
infection before inoculation experiments could be successfully conducted. 
Among the substances tried were hydrogen peroxid, hydrochloric acid, 
sulphuric acid, formalin solution, formaldehyde vapor, and hot water. 
Peroxid solution (6 per cent) was used for varying periods up to one hour. 
The seed was then sown in sterilized soil and watered with distilled 
water. The pots were protected from infection, but damping-off was in 
no degree checked, and Phoma betae was invariably isolated from the 
diseased seedlings (PI. XVII). 

Hydrochloric acid was employed in various concentrations up to a 
specific gravity of 20° B. for 15 minutes. The seed was then rinsed in 
sterile water, followed by lime water, which in turn was followed by 
sterile water. This treatment was without effect upon the vitality either 
of the seed or of the fungi. 

Sulphuric acid was used in various strengths up to full concentration 
for one hour. The treated seed germinated strongly and from 24 to 48 
hours earlier than the untreated control, but there was no decrease in 
the amount of damping-off. 

Fonnalin solution was employed up to concentrations of 2 per cent of 
formaldehyde for various intervals up to one hour. This seriously injured 
the viability of the seed, but afforded no check to the disease. The 
results with formaldehyde vapor are inconclusive, since they lack uni- 
formity. 

The method finally settled upon for experimental work was one em- 
ployed by Peters (7, p. 273-274), which consists of heating the seed in 
water at 60° C. for 10 minutes, promptly drying superficially upon filter 
papers, so as to prevent germination, and after an interval of 24 hours 
heating a second time for 10 minutes at 60° C. The seed treated in this 
way and sown in steriUzed soil, watered with sterile water, and protected 
from outside infection remained practically free from disease. Not more 
than one seedling in three or four hundred was infected with Phvma 
beiae. The percentage of germination is unquestionably lowered by this 
treatment, but it is the only method tried by which inoculation experi- 
ments could be controlled. It does not appear to be a method which 
could be applied on a commercial scale. 

METHODS OF INOCULATION 

Inoculation experiments were carried out in pots either in the labora- 
tory or usually in the greenhouse, using seed treated in the manner just 
described, and with soil sterilized by heating three or four hours in the 
autoclave under a pressure of from 12 to 15 pounds on two, or usually 
three, consecutive days. Inoculations were made in the soil or upon the 
seed at the time of sowing, except when otherwise stated. A^arious 



May 15. 1915 Seedling Diseases of Sugar Beets 139 

methods of inoculation were employed, but the results were uniformly the 
same. Either suspensions of spores or mycelial growth on various cul- 
ture media, such as agar, com meal, beet petioles, and sterilized beet 
blocks, were employed. The last method — that is, with beet blocks — 
was perhaps the most satisfactory and convenient. The com-meal 
cultures appeared to exercise an unfavorable physiological action, pos- 
sibly because of the bacterial growth which they fostered; so this 
method was discarded. 

Inoculation experiments were invariably controlled by a considerable 
number of uninoculated pots. In a few instances disease occurred in 
the controls. In such cases the causal organism was determined, but 
the entire series was abandoned as an inoculation experiment, even 
though the presence of an intruder could be explained readily through 
the agency of insects and earthworms. It was the invariable custom to 
recover the fungus from the damping-off seedlings by the method already 
described (PI. XVI and XVII) and to reinoculate and recover through 
from four to six generations of seedlings. 

As reported in a former note (12), four fungi have been found to stand 
in causal relation to seedling-beet troubles. These are Phoma beiae (Oud.) 
Fr., a species of Rhizoctonia, regarded as identical with the form 
described as Corticium vagum B. and C, var. solani Burt., Pythium 
debaryanum Hesse, and a fungus originally reported as Aphanomyces 
laevis De By., but which has since been found to be new. 

PHOMA BETAE 
TAXONOMY 

Frank (16, 17, 18, 20) established the relation of Phoma betae to 
heart-rot of the sugar beet in 1892. The following year Kriiger (25, 26), 
working in the same field, demonstrated its causal relation to damping- 
off. He found the fungus fruiting abundantly on all parts of diseased 
beets and held it to be identical with the fungus which had previously 
been observed on various portions of the cultivated varieties of Beta 
vulgaris L. 

Oudemans (29, p. 181) had observed what appeared to be the same 
fungus fruiting upon leaf spots of old beets and applied the name "Phyl- 
losti£ia betae." Prillieux (35, p. 19) observed the fungus on leaf blades 
and decaying heart leaves, as well as upon typical spots on the leaf, 
and applied the name " Phyllosticta tabifica." Saccardo recognizes the 
names "Phyllosticta betae Oud." and "Phoma betae Rostr." The latter 
name is given on the authority of the following paragraph from the pen 
of E. Rostrup (41, p. 323): 

Eine zweite, an Runkelruben auftretende Phoma habe ich zuerst in meinem 
Jahresbericht iiber Krankheiten der Kulturgewachse im Jahre 1888 (Tidsskrift for 
Landokonomi. R. 5, Bd. 8, S. 746) [40] unter dem Namen Phoma spha^rosperina 
beschrieben. Weil sich aber herausstellte, dass dieser Name schon im Jahre 1885 
einer ganz anderen Art gegeben war, naimte ich spater den Pilz Phoma Betae. 



140 Journal of Agricultural Research voi. iv. No. i 

No reference to the publication in which this change of name was 
announced is given, and efforts to find it have failed. Moreover, Lind 
(28, p. 415), who had full access to Rostrup's specimens and publica- 
tions, lists Phoma betae Rostr. under Phoma betae Fr. as a synonym. 
Frank suggested the name "Phoma betae" in the article previously cited 
(16), published in 1892, which contains a description of the fungus, 
accompanied by figures and a somewhat extended discussion of the 
root-rot produced by it on the sugar beet. In view of the established 
identity between Phoma and Phyllosticta on sugar beets it would 
appear that Oudemans' description in 1877 (29) has first claim to 
priority. 

For these reasons it seems proper and convenient to retain the name 
which has persisted in most general use in literature, but with a correc- 
tion to insure proper acknowledgment to Oudemans. The name "Phoma 
betae (Oud.) Fr." is therefore used in this paper. Pool and McKay, who 
agree in the justice of this usage, also employ it in a current paper (34). 

Neither Frank (17) nor Kriiger (25, 26) were able to find evidences 
of a perfect stage of this fungus in their cultural studies. Peters (31, 
32, 33) also failed to find sexual fruits, and the same is true of the work 
of the writer. It should be pointed out, however, that Rostrup (40, 
p. 746) believed Sporodesmium pulrefaciens Fuck, to be a perfect stage of 
Phoma betae, and Prillieux and Delacroix (37) regarded Phoma betae as 
the pycnidial form of Sphaerella tabifica Delacr. 

IDENTITY OF PHOMA AND PHYLLOSTICTA ON THE SUGAR BEET 

Hedgcock (22) has presented evidence by cross-inoculation of the 
identity of Phyllosticta and Phoma on the sugar beet. He grew beets 
from seed treated with concentrated sulphuric acid for 30 minutes, fol- 
lowed by an alkali, and successfully produced Phyllosticta spots by 
spraying upon the leaves spores of a Phoma culture isolated from decay- 
ing beets. Beets whose leaves were covered with Phyllosticta were 
placed in a dry cellar and held under observation for two months, during 
which time the characteristic black rot of Phoma passed from the leaf 
petioles to the crown of the beet. 

While Hedgcock's conclusions are undoubtedly correct, the seed 
treatment he employed does not destroy the viability of Phoma, and it 
will be shown later that beets whose foliage was free from visible evi- 
dence of Phyllosticta decayed from Phoma when they were placed in a 
relatively dry environment. The case may be strengthened, therefore, 
by the presentation of the additional evidence now available. Cultures 
from Phyllosticta spots, as well as from decayed beets and from damped- 
off seedlings, have been found equally capable of producing damping-off 
of sugar beets, and a somewhat extended study of the morphology of 
the fungus from the three sources mentioned has revealed no differences 



May IS. 191S Seedling Diseases of Sugar Beets 141 

between them. The Phyllosticta cultures employed were supplied by 
Miss Venus W. Pool, of the Rocky Ford (Colo.) field station. Pool and 
McKay (34) , who worked with Phoma cultures isolated by the writer from 
decayed sugar beets, found them capable of producing the characteristic 
leaf spots as readily as cultures isolated from the Phyllosticta pycnidia. 
The fungus, however, is not an aggressive leaf parasite, but does its 
greatest injury on the root. 

SOURCES OF INFECTION 

The source of original infection appears to be the seed. It has been 
generally recognized in Europe for years that seed infection with Phoma 
betae is universal. As American growers are using European seed 
almost exclusively, it follows that the disease is constantly being intro- 
duced into the United States on seed. A very large number of samples 
of both European- and American-grown beet seed have been examined 
for the presence of this and other pathogenic forms. With the excep- 
tion of one single lot of seed, the examination of 100 seed balls by the 
seedling method has invariably demonstrated the presence of Phoma 
betae. Reexamination of this one lot, which was American-grown, 
revealed the presence of the fungus in it also when larger samples were 
tested. 

Frank (18, p. 180, 272-293) believed the fungus capable of living over 
in the soil by means of its spores, but Peters (7, p. 278-286) holds that 
it can do so only when fragments of beets are present to support mycelial 
growth. A large number of trials of soil in America made by means of 
seedlings growing in it from pasteurized seed indicate that Phoma does 
not remain viable in the soil after the decomposition and disintegration 
of its host. Field soils containing decaying beet fragments occasionally 
yield cultures of the fungus in the spring of the first year following beets, 
but, as a rule, even seriously beet-sick soils fail to give them. Samples 
have been examined from Virginia, District of Columbia, Michigan, 
Wisconsin, Kansas, Colorado, Utah, and California. 

MORPHOLOGY OF THE FUNGUS 

Several hundred cultures of the fungus have been isolated and grown 
upon media (PI. XVII). No constant dififerences in cultural characters of 
strains from the various sources have been observed. It is readily culti- 
vated upon a great variety of media, although on many of these it 
develops mycelium only. It fruits abundantly upon string-bean agar 
(PI. XVII, fig. 2) and this medium has been used for purposes of identifica- 
tion and for measurements of pycnidia and spores. It is evident that the 
curves which might be plotted from the following tabulated results of 
measurements would be irregular and consequently that they would 
probably be changed by increasing the number of pycnidia and spores 



142 



Journal of Agricultural Research 



Vol. IV. No. 2 



measured (Table I). Of i8i pycnidia measured the smallest was 125/4 
and the largest 635/i in diameter. The largest number fall between 225 
and 325/1. 

Table I. — Variation in size of iSl pycnidia 0/ Pkoma beiae 



Number 


Variation in 


Number 


Variation in 


measured. 


diameter. 


measured. 


diameter. 




I' 




1^ 


I 


125 


II 


351 to 375 


4 


126 to 150 


5 


376 to 400 


14 


151 to 175 


10 


401 to 425 


7 


176 to 200 


5 


426 to 450 


31 


201 to 225 




451 to 475 


21 


226 to 250 




476 to 500 


10 


251 to 27s 




501 to 525 


27 


276 to 300 




526 to 550 


19 


301 to 325 




551 to 63s 


II 


326 to 350 







The pycnospores showed quite wide variations in size. The shortest 
of 204 spores measured 3.8 and the longest g.^u. Practically all fell 
between 4.1 and 7/1, as shown in Table I. 

The width of the pycnospores varied from 2.6 to 4.3/(. The single 
exception to this case is a spore which measured 4.9/( in width. Table 
II will show the distribution of numbers within the limits given. 

Table II. — Variation in size of 204 pycnospores of Photna betae 

LENGTH 



Number 
measured. 


Variation. 


Number 
measured. 


Variation. 




li 




/^ 


I 


3-8 


14 


6. I to 6. 2 


4 


4. I to 4. 2 


II 


6 


3 to 6. 4 


3 


4. 3 to 4. 4 


6 


6 


5 to 6. 6 


2 


4. 5 to 4. 6 


6 


6 


7 to 6. 8 


14 


4. 7 to 4. 8 


7 


6 


9 to 7. 


13 


4. 9 to 5. 


I 




I to 7. 2 


22 


5. I to s. 2 


I 




3 to 7. 4 


21 


5- 3 to s. 4 


2 




S to 7. 6 


24 


5- 5 to s- 6 


2 




7 to 7. 8 


22 


5- 7 to 5. 8 


I 




9 to 8. 


25 


5. 9 to 6. 


2 


9 


3 to 9. 4 



5 

43 
49 
42 



6 to 2. 
8 to 2. 
ot0 3. 
2 to 3. 
4 to 3. 



22 

17 

7 

3 



3. 6 to 3. 
3- 8 to 3. 

4. o to 4. 

4. 2 to 4. 

4.9 



May 15. 1915 



Seedling Diseases of Sugar Beets 



143 



VITALITY IN CULTURE 

Phoma betae exhibits long vitality in culture, as is shown by the follow- 
ing tests. 

On July 2, 1 91 3, old cultures which had been apparently air-dry for 
months were opened under sterile conditions, and into each a portion of 
string-bean agar was introduced. The tubes were then placed to harden 
in such a position as to leave the old culture partly submerged. Table 
III gives the age of the cultures and the results after six days' incubation. 

Table III- — VUalHy of Phoma beiae in culture 



Phoma 


Num- 


Age of 




Phoma 


Num- 


Age of 




strain. 


ber. 


culture. 




strain. 


ber. 


culture. 








Days. 








Days. 




Strain 3. .. 


39 


413 


Good growth 
and pycni- 
dia. 


Strain M.. 


1.304 


315 


Good growth 
and pycni- 
dia. 


Strain A. . . 


423 


372 


Do. 


Strain 3 . . . 


64 


413 


No growth. 


Strain T-. 


564 


3S8 


Do. 


Strain 3 . . . 


40 


413 


Do. 


Strain "j . . 


996 


315 


Do. 


Strain 3 . . 


281 


404 


Do. 


Strain E . . 


I, 296 


315 


Do. 


Strain 3 . . 


3S6 


404 


Do. 


Strain J . . 


1,301 


315 


Do. 











INOCULATION EXPERIMENTS ON SEEDLINGS 

The strains used in inoculation experiments are 24 in number, obtained 
from the following sources: 

Direct isolation from sugar-beet seed by the moist-chamber method, i. 

Indirect isolation from sugar-beet seed through damping-off seedlings 
in sterilized soil, 2. 

Direct isolation from Phyllosticta leaf-spot, 2. 

Isolations from various sources such as beet leaves, beet seed, and 
beet-sick soil at Rocky Ford, Colo., 13.' 

Isolations from beets having heart-rot, from Colorado, i ; Wisconsin, 
2; South Dakota, i. 

Isolations from seedlings grown in sterilized soil, inoculated with 
decayed beets, 2. 

The inoculation experiments upon seedlings were carried out in the 
manner already described, invariably yielding positive results. There 
appeared to be no decrease in virulence from carrying the fungus in 
culture 14 months. 

The first development of damping-off in the pots occurred usually 
about the third day after the seedlings broke the ground and continued 
till about the time they developed their third or fourth pair of leaves 
(PI. XVIII, fig. 2). The method followed was to sow 100 seed balls per 

' These cultures were kindly supplied by Miss Venus W. Pool, of the Bureau of Plant Industr>'. from 
the Rocky Ford (Colo.) Seld station. 

90271°— 15 4 



144 



Journal of Agricultural Research 



Vol. IV, No. 1 



pot and to examine daily for damping-ofif. Whenever disease occurred, 
the plants affected were removed and a record made of their number. 
The period of greatest susceptibility seemed to be passed by thi time 
the third set of leaves appeared. After a sufficient period the remaining 
plants were harvested and examined for signs of infection on the roots. 
The following record (Table IV) of a typical series illustrates thf; 
method and gives a good idea of the average results. 

Table IV. — Results of inoculation experiment with Phoma betae 









[Series of Jime 27 


1912: 














Phoma strain. 


Appeared 
above- 
ground OQ — 


Number of seedlings diseased on July — 


Number har- 
vested on July 29. 


3 


4 


5 


6 


7 


10 


12 


■s 


17 


Dis- 
eased. 


Healthy. 


Strain C 


July I 
. . .do 






3 
10 

3 

2 

20 


5 
7 
6 
8 

13 
5 

12 
8 

22 


6 
8 

3 
12 
8 
6 


4S 


18 

9 

12 
27 
16 

9 
II 
21 

5 


19 
7 

13 

17 

2 

9 



iS 




5 
3 
4 
6 


10 


14 





2 

4 
2 

I 





4 
S 
7 
7 

S 


18 


Strain E 




7 
2 

I 
24 


3 
30 
13 



14 


Strain B 


do , 




Strain A 


July 2 
J"^^o ' 


2 


Strain D 

Strain F 


Strain H 


...do 




7 


44 


Strain G 


. ..do 




52 
S 


12 


Do 


...do 




5 


II 


7 

III 


Control . . . 


July 2 
. . .do 




Do 






















148 



























The plants described as diseased were typical root-sick beets. There 
was nothing about their appearance aboveground in the pots to indicate 
the presence of the fungus, but in the field such seedlings may often be 
detected from the fact that they appear to be suffering from lack of 
moisture. This type of disease is almost universal under field conditions 
and is far more common than damping-off. Histological studies upon 
such material, to be published in a subsequent paper, revealed the sig- 
nificant fact that it often carries the pycnidia and sometimes the vege- 
tative mycelium of the fungus. 

The number of seedlings developing in control pots was, as a rule, 
larger than the total number developing in inoculated ones. This is to 
be explained by the fact that some of the seedlings were attacked before 
they broke the ground and in consequence were unable to push through 
the soil. A careful examination of the surface soil in inoculated pots 
now and then revealed such seedlings in a state of more or less complete 
decay. 



PHOMA FIELD-ROT AND STORAGE-ROT FOLLOWING SEEDLING INFECTION 

When diseased plants were allowed to remain in the pots and were 
held under as favorable conditions as possible, a large proportion of 
them eventually survived and sent out new roots. This condition is 



May IS, 191 5 Seedling Diseases of Sugar Beets 145 

often observed in commercial fields, and it is probably safe to say 
that, under advantageous conditions of climate and cultivation, 75 
per cent of the beets attacked by Phoma beiae are not killed, but throw 
off the parasite sufficiently to make a good growth while continuing to 
carry the fungus in a dormant condition upon the crown. When the 
vitality of the host is sufficiently reduced, the parasite may become active 
again and develop either in the root, where it causes a black rot, or on 
the aerial portions of the plant, where it causes a spot disease, which, 
while it does not injure the host to an appreciable extent, enables the 
fungus to infect the seed growing on mother plants. The rot is, of course, 
more serious to the plants attacked. Cases of this so-called heart-rot in 
the field have been very destructive at times in certain sections of 
Europe and are not infrequent in America. Important instances of 
its occurrence in Michigan, Wisconsin, and Colorado, and a less serious 
case in New York, have come to the writer's attention. Material from 
the three States first mentioned was available for study. The fungus 
was easily secured in pure culture from the beets that were partially 
decayed by the black rot typical of the disease (PI. XVIII, fig. 1). 
Many roots presented unmistakable evidence of having been diseased 
in the seedling stage. In some cases the original taproot had been de- 
stroyed, and only a knob of tissue just below the crown had survived. 

Additional evidence that the fungus is capable of living upon its host 
for a long time in an inconspicuous and apparently harmless form until 
those conditions appear which are favorable to its development is readily 
found upon examination of beets in storage or those which have been 
kept over for seed purposes. Such examination in the spring has never 
failed to reveal the presence of the fungus. Sometimes the entire root 
is destroyed, but more frequently beets that are apparently healthy may 
be found to show black spots in certain sections in or near their vascular 
tissue, especially in the top of the crown. These areas usually develop 
longitudinally and are frequently confined to the vicinity of a single 
vascular bundle (Pi. XIX). When the conditions of storage have been 
imfavorable, the rot may assume an epidemic form and lead to the total 
destruction of roots which were apparently healthy and sound when 
placed in storage. 

INOCULATION EXPERIMENTS ON GROWING BEETS 

Evidence that the infection takes place only in the seedling stage or 
through the leaves in old age is found in the results of inoculation experi- 
ments made with cultures of Phoma beiae. In August, 191 2, 100 ap- 
parently healthy beets growing in the field at Madison, Wis., were 
inoculated. A portion of the infections were made directly upon the 
uninjured crown with vegetative cultures upon beet blocks. Other 
inoculations were made through wounds near the surface of the soil and 



146 Journal of Agricultural Research voi. iv, No. 2 

still others through wounds on the petiole or in the heart of the crown. 
In no case was there any evidence of rot in the field or at the time of 
harvest. It was at first believed that climatic conditions were respon- 
sible for the failure. However, the beets were placed in storage. The 
following spring they were examined for evidences of Phoma beiae by 
culture methods. None of the beets had been destroyed; indeed, most 
of them appeared to be perfectly sound until they were opened, when the 
black lines previously mentioned appeared in the vascular regions. 
Cultures were obtained from each of the infected beets, except two. These 
results were at first interpreted as an indication that the inoculations 
made in August had produced infection which had persisted on the sur- 
face and penetrated the roots in storage, but subsequent developments 
throw doubt upon this conclusion and indicate that the infection oc- 
curred much earlier. About half a ton of beets grown as controls had 
been placed in storage beside the infected material, but in a lower rack. 
Evidences of rot were observed in only half a dozen of these beets, and 
they yielded cultures of Phoma beiae. It was noted at the time of 
examination that the control beets, which had been kept nearer the 
surface of the soil, were all firmer than the inoculated material; but 
unfortunately no significance was attached to this fact at the time, and, 
with the exception of 12 of the control beets, the entire lot of material 
was sent to the feeding sheds. 

A few weeks later a large quantity of mother beets grown in the vicinity 
of the experimental field from western seed was found to be seriously in- 
jured by the Phoma rot, practically every beet showing more or less evi- 
dence of it. These beets had been bored for analysis in the fall, so that 
any evidence of infection at that time would have been apparent. The 
decay did not originate from infection in the wound made by boring, as 
may be seen readily by reference to the illustration (PI. XIX). In the 
large majority of cases the rot evidently started from the crown, although 
there were cases of pockets of decay on the sides or even at the tip of the 
beet. In some instances dark streaks could be traced from the crown to 
decayed areas in the lower portion. This led to the belief that the decay 
in beets inoculated with Phoma betae was due to infection occurring in 
the seedling stage and that its development was fostered by the less 
favorable, dryer conditions of storage tp which they were submitted. 
Additional evidence for this belief is to be found in the results of the 
inoculation experiments with Rhizoctonia (p. 153), since the Phoma 
rot appeared upon this material also. Moreover, of the few control beets 
saved from the feeding sheds all but three developed Phoma decay during 
the late spring and early summer, and cultures of Phoma betae were 
secured from darkened bundles in the crowns of these three. It might 
be urged that the infection reached the crowns of these beets by way of 
the petioles from Phyllosticta upon the leaves. This seems a very prob- 
able means of infection, but appears unlikely in the instances above cited, 



May 15, 191S Seedling Diseases of Sugar Beets 147 

since Phyllosticta spots were at no time observed upon the foliage of the 
beets in question, which were grown in isolation and were under daily 
observation. The following season (191 3) inoculations were made on 
beets grown outdoors at Madison, Wis., in pots filled with soil from Garden 
City, Kans., from Rocky Ford, Colo., and from Madison, Wis. Other 
beets grown in the usual way in the field at Madison, at Garden City, and 
at Rocky Ford were inoculated. In all cases this was done by placing a 
large fragment of actively growing culture on sterilized beet blocks upon 
the crown of the beet near the heart and a second portion in direct con- 
tact with an abrasion on the crown just beneath the surface of the soil. 
Through the courtesy of colleagues at Garden City and Rocky Ford it 
was possible to have the beets watched at these points as carefully as 
were those at Madison. At no time during the season did evidence of 
infection appear on any of the beets under observation. 

Two lots of beets were grown in 191 3 from pasteurized seed. One lot 
was isolated from other beets so as to be protected from infection. These 
beets were stored in the fall in a warm basement, which offered very 
favorable conditions for the development of Phoma storage- rot, as shown 
by previous experience. They were examined from time to time during 
the winter, spring, and summer for evidences of Phoma betae, with nega- 
tive results. 

The other lot of seed was sown in proximity to breeding stock and 
mother plants known to be infected with Phoma betae, and stored in a 
cellar with infected material. These beets developed Phoma rot during 
the winter. Phyllosticta appeared on seed plants grown from some of 
these roots during the summer of 1914, and the seed produced was found 
to carry the pycnidia and spores of Phoma. 

PERPETUATION OP THE FUNGUS 

The results of the various experiments coupled with field observations 
lead to the opinion that Phoma betae is capable of infecting Beta vulgaris 
L. only during periods of especial susceptibility, such as the early seed- 
ling stage, or, in the case of the leaf, during physiological old age. It 
may also be that the root is susceptible to infection during periods of low 
vitality induced by unfavorable environment, but experimental proof is 
lacking. It does appear, however, that this fungus is entirely capable 
of living for a long time in a hidden condition upon the crown of the 
beet, ready to take advantage of any diminished vitality in its host. 
After infection has once occurred, the parasite may remain present in a 
viable though inconspicuous condition, although the host appears to have 
completely overcome the disease. The Phoma field-rot in the summer 
and fall of 1913, in Wisconsin and Colorado, respectively, developing in 
the first instance under conditions of excessive moisture and in the sec- 
ond under severe drought, may be explained in this way. The crown 



148 Journal of Agricultural Research voi. iv. no. , 

infections originating from the seed readily explain the source of the spores 
producing the outbreaks of Phyllosticta, which appear to be much more 
common in regions of low humidity, where, as Pool and McKay (34) have 
shown, viable spores of this fungus are common in the air. In this con- 
nection, attention should be especially called to observations during the 
seasons of 1912 and 1913 in Colorado, Idaho, and Wisconsin, since they in- 
dicate a direct connection between the occurrence of Phyllosticta on the 
leaves and seed stalks of mother beets and the presence of Phoma on the 
seed they produce. Phyllosticta was quite prevalent in the Idaho-Colorado 
region, but escaped detection by the same observer in Wisconsin. Tests 
upon seed produced in these regions during both seasons have shown 
that the more western seed was quite generally infected to an extent 
comparable to that from European sources, while that grown in Wis- 
consin showed only a very slight infection. 

Pool and McKay, who kindly continued the observations at Madison 
during the absence of the author in the season of 1914, found the Phyl- 
losticta form on the leaves and stalks of seed beets and also on first-year 
beets. In the absence of fruits the causal fungus was identified by cul- 
tural methods. In other instances pycnidia were produced. The spots 
were, as a rule, less clearly defined and less numerous than those in the 
Idaho-Colorado region, which are similar to those seen in Europe in 1914, 
where they were common on both field and mother beets. Since the 
leaf form of the disease occurred in Wisconsin in 191 4, it is probably safe 
to assume that it existed there on seed beets, undetected, in the two 
preceding years. However, if the absence of Phyllosticta infection in 
Wisconsin in 1912 and 1913 be assumed, the presence of the small amount 
of Phoma hetae on the seed produced there may still be accounted for in 
at least three different ways. The seed balls may have been infected at 
any time between blossom and maturity by air-borne spores developing 
in the crown. The fungus may have spread from the crown of the 
mother plants on the surface of the seed stalks to the racemes and infected 
the fruit, or it may have passed through the vascular system of the stem 
to the seed. 

CONTROL OF THE FUNGUS 

It is apparent that Phoma betae is one of the most serious obstacles 
which the growers of beet seed in America have to face. Its ravages on 
mother beets during the winter may be largely overcome by favorable con- 
ditions of storage, but in case the mother beet escapes destruction the 
infection remains to proceed to the leaves and seed stalks and to infect 
the seed. Since the fungus sometimes inhabits the vascular region of 
the root, it may possibly progress through the stem, as well as on the 
surface. In any event, it is an undoubted fact that it finds its way into 
the young seed ball, where it starts with the seed upon another 2-year 
cycle. 



May IS. 191S Seedling Diseases of Sugar Beets 149 

From what has been said regarding sources of infection, it appears 
that ordinary attention to rotation should eliminate danger from soil 
infection, but that all seed at present available is heavily infected. The 
only hope of control therefore lies in one or more of three alternatives: 
(i) The natural resistance of the beet to the attacks of the fungus, (2) 
seed treatments, (3) the production of disease-free seed. 

From the facts that the period of infection with Phoma beiae is 
normally confined to a relatively short period in the seedling stage and 
that infected plants frequently throw off the attack, proper attention to 
cultural conditions would seem to offer hopeful prospect of control. 
European experience has demonstrated the value of such methods. 
Indeed, some prominent agriculturists have denied the pathogenicity of 
Phoma betae because of their success in preventing damping-off and root 
sickness by proper cultivation and fertilization. From this they have 
argued that the cause lies in unfavorable cultural conditions rather than 
the presence of parasites. The truth undoubtedly is that unfavorable 
environment is a predisposing cause which so weakens the beet that it is 
unable to compete successfully with the fungus. When planted in good 
soil, which has been well prepared and suitably fertilized, the seed germi- 
nates promptly and the young plants pass rapidly through the period of 
danger. Early cultivation at this stage to insure proper aeration of the 
roots is beneficial. The studies upon control by means of cultural 
methods and fertilizers demonstrate the value of properly prepared soil 
and thorough cultivation promptly after the seedlings come through the 
ground. There is no doubt that frequently an infected stand may be 
saved in this way. In Europe the use of phosphoric acid and potash 
has given good results. The question of soil reaction has also been found 
very important. Applications of lime on certain types of acid soil result 
in almost complete control. This may also prove to be the case in 
America, but the point can be determined only by local experiment. 

As has already been said, the only method of seed treatment which has 
given satisfactory results in pot experiments is seed pasteurization. 
Experimental work to test the efficiency of this method in field practice has 
been attempted. It is not believed that a method of treatment as 
difficult to carry out as pasteurization will prove useful except in the 
hands of experimentalists and for experimental purposes. It is apparent 
that seed must be treated in small lots and with extreme care in order 
to secure the desired result. If temperatures much above 60° C. are 
employed, the injury to the seed becomes serious. Temperatures below 
60° are ineffective. The substitution of one treatment for two is like- 
wise unsuccessful. Attempts to apply the treatment to samples of seed 
of even 5 pounds have not been altogether satisfactory, but appear to 
hold the fungus in check. 

One experiment in seed treatment carried out under field conditions 
where epidemic development of root sickness has annually occurred for 



1 50 JournaU of Agricultural Research voi. iv, no. j 

several years will illustrate the point. A half-acre field was prepared. 
Five pounds of pasteurized seed were sown on one quarter-acre and five 
pounds of untreated seed on the other. As soon as the seedlings were 
well out of the ground, examination was made for root sickness and 
damping-off. No signs of damping-off were seen, but considerable root 
sickness was in evidence on both the treated and untreated sections. 
Cultures were started in the field by treating the seedlings for one minute 
in a triturate of citric acid and bichlorid of mercury in water of such 
strength as to give a i to i ,000 solution of sublimate. They were then 
transferred to test tubes of sterilized water and were brought to the 
laboratory, where they were plated. A period of 36 hours elapsed 
between the treatment with the bichlorid of mercury and the plating. 
From the untreated seed 95 seedlings yielded the following results: Phoma, 
29; Fusarium, 19; Macrosporium, 2; Mucor, 6; miscellaneous, 18; no 
growth, 21. From the treated seed 69 seedlings yielded: Fusarium, 23; 
an unidentified ascomycete, 1 1 ; Macrosporium, 2 ; Mucor, 2 ; Penicillium, 
i; miscellaneous, 8; no growth, 22. Phoma betae was not found in the 
treated lot. The long interval before plating undoubtedly accounts for 
the large amount of Fusarium and perhaps also for the failure to secure 
growth in many cases. 

The average results secured from prompt plating may be seen from the 
following series, which was from the same locality but was made two weeks 
earlier. Many of these were plated immediately. Most of the Fusarium 
resulted from seedUngs which were carried in the water blanks for half a 
day or more. Two hundred seedlings yielded cultures as follows : Phoma, 
149; Fusarium, 29; Pythium, 3; miscellaneous, 11; no growth, 8. It 
therefore appears that, while seed pasteurization may be employed suc- 
cessfully to rid seed of Phoma betae for experimental purposes, it is not 
applicable on a commercial scale. Moreover, such treatment does not 
guarantee freedom from physiological root sickness associated with sap- 
rophytic fungi, since the vitality of the seedlings seems to be lowered by 
pasteurization. 

A realization of these facts suggests the necessity of clean stock for 
breeding purposes. It would seem that if the growers of elite strains 
could rid their stock of this parasite it would thereafter remain clean, 
provided a reasonable rotation were observed and the seed fields were 
sufficiently isolated to escape reinfection with Phyllosticta. Danger 
from this source would diminish with the increase in the supply of clean 
seed. The experimental work already reported has shown the possi- 
bility of ehminating the fungus from plants grown in isolation from pas- 
teurized seed. These plants would produce clean seed which could again 
be sown in isolation from infected stock and made the basis for a seed 
supply for an entire community, from which the fungus would be elimi- 
nated. This community could be employed as a breeding center where 
the entire seed supply of a factory could be grown, and one of the most 



May 15. 1915 Seedling Diseases of Sugar Beets 151 

serious fungous pests of the sugar beet eliminated from its territory. 
Since sugar companies have absolute control over the sources of seed 
supply of their growers, it is quite possible for a company producing even 
a portion of its own seed to maintain an area of quarantine within any 
portion of its territory where it does not compete with other companies 
for acreage, provided table beets and mangel-wurzels are not allowed to 
bring in the infection. 

RHIZOCTONIA 

The genus Rhizoctonia has been used to include a group of sterile 
fungi, more or less closely related morphologically. Much confusion 
exists regarding the identity of the various forms, and there is likewise 
great diversity of opinion as to the pathogenic properties of the members 
of the group. To make clear, especially to foreign investigators, the 
identity of the fungus under consideration in this paper, a brief discus- 
sion of the literature seems essential. The name "Rhizoctonia" was 
first applied by De Candolle (8) in 18 15 to a fungus on alfalfa. He 
eventually distinguished three species, R. crocoruni, R. medicaginis , and 
R. mali. During the following 35 years various workers described a 
series of diseases caused by similar fungi, which were referred to this or 
other genera. In 1851 Tulasne (43, p. 188) united the known forms of 
Rhizoctonia into one species under the name "Rhizoctonia violacea." 
This classification has been followed by many workers. 

In 1858 Kiihn (27, p. 222-249) published an account of three species, 
R. solani, R. medicaginis, and R. crocorum. He distinguished between the 
two forms first mentioned by the difference in appearance of the sclerotia, 
those of R. sola-id being smooth, and those of R. medicaginis, woolly. 
He mentions R. medicaginis as being parasitic on the beet and carrot, 
as well as alfalfa, and states that the fungus produces a reddish brown 
or purplish color in the cells of the beet. This is the first mention of 
Rhizoctonia on the beet, and it is likewise the first mention of the fungus 
in Germany. Saccardo has included Kiihn's species under R. violacea, 
while Giissow (21), who described a disease on potatoes and alfalfa in 
England due to Rhizoctonia, considers R. solani Kiihn to be identical with 
R. violacea Tul. Eriksson (14) in 1903 published the results of inocula- 
tion work on various hosts, including the sugar beet. He designated his 
fungus as R. violacea, but later reclassified it as Hypochnus violaceae (Tul.) 
Eriks. (15, p. 421-430). He believed there were biological forms of it, 
since the form on carrot attacked the beet with more virulence in the 
second generation than in the first in which it was carried on that host. 

Atkinson (i) in 1892 described a damping-off of cotton due to a 
sterile fungus later classified as Rhizoctonia. Balls (2, 3) has found 
the same disease in Egypt, and Shaw (42) has more recently reported it 
from India. In the meantime Duggar (10, p. 344) described the same 
fungus as a damping-off parasite of the sugar beet, and Pammel (30) 



152 Journal of Agricultural Research voi. iv, No. > 

reported a root-rot of beets in Iowa that he believed to be due to Rhi- 
zoctonia hetae Kiihii. The fungus, however, appears to be indistinguish- 
able from the one which Atkinson and Duggar, respectively, had reported 
as a damping-o£f agent on cotton and sugar-beet seedlings and from 
forms of Rhizoctonia upon a variety of hosts throughout the United 
States, acting either as damping-off agents or as the causes of other forms 
of plant diseases. Rolfs (38, 39), working with the fungus on the potato 
in Colorado, found a fraiting stage which he designated as Corticium 
■vagum B. and C, var. solani Burt. He was unable to produce the 
Corticium in culture, but the growth from spores yielded typical Rhizoc- 
tonia mycelium, and infections on living plants with Rhizoctonia gave 
rise to Corticium. Shaw observed the fruiting stage on the groundnut 
and later succeeded in producing it by artificial infection on that host. 
European workers have referred what appears to be the same basidial 
fonn to Hypochnus solani. 

Shaw (42) found marked differences in the character of sclerotia pro- 
duced by his strains. One which formed small black sclerotia more or 
less differentiated into cortex and medulla he designated as R. solani 
Kiihn. The structure of the sclerotia of the other Rhizoctonia which 
he designated only as Corticium vagiim B. and C. appears to correspond 
closely with that of those obtained in America in cultures and less fre- 
quently on the host. He believed this Corticium to be identical with 
the form common on potatoes in America, but was unable to see justi- 
fication for referring it to R. solani Kuhn. Furthermore, he believed 
R. violacea Tul. to be a compound species, possibly including R. solani 
Kiihn and the Corticium, since Prillieux (36, t. 2, p. 144) described 
R. violacea Tul. as possessing two distinct forms of sclerotia, one of which, 
according to Shaw, is similar to those of R. solani Kiihn and the other 
to Corticium vagum. 

A form of crown rot on the sugar beet caused by Rhizoctonia violacea 
Tul. is well known in certain sections of Europe, but rot from Rhizoctonia 
solani is unknown there. This fact has led many students to question 
the identity of the fungus causing the rot of the beet in America. The 
organism here considered is distinctly different from the Rhizoctonia 
violacea Tul. type as the writer saw it in Europe on living or preser\'ed 
material from a variety of hosts, including beets, carrots, potato tubers, 
alfalfa, and asparagus, but it appears to be identical with the Rhizoctonia 
solani type which forms the sclerotia on the potato in Europe and 
America. These two fungi when studied on the same host differ in the 
character of the disease produced, in their appearance on the plants, and 
in the histological relation of the parasite and host. The two are so 
distinct in these characters on both the beet and the potato that it seems 
impossible for one who has seen both types to confuse them. The cul- 
tural relations of the two are also distinctly different. Rhizoctonia solani 
is readily cultivated on a variety of media, but all attempts to put 



Mayis. I9IS Seedling Diseases of Sugar Beetr 153 

R. violacea into artificial culture have thus far failed, though many 
different workers have undertaken it. So far as can be detennined from 
the literature, the American fungus also appears to be identical with 
Shaw's (42) Corticium vagum B. and C, and it is indistinguishable in 
culture from a strain isolated in Ireland by Pethybridge from a single 
spore of Hypochnus on the potato, and kindly contributed by him under 
the name ' Hypochnus solani." 

The fuiigus is characterized by a septate mycelium the branches of 
which in young cultures are either parallel to or inclined at a more or 
less acute angle to the direction of growth of the parent branch. There 
is a constriction where the branch unites with the old hypha and a 
septum is formed a few microns from the point of origin. The threads 
are hyaline when young, becoming a yellowish brown with age. In 
mature cultures the branches are usually arranged very nearly at right 
angles to the parent thread at the point of origin. In culture and less 
frequently upon the host it forms sclerotia, which vary greatly in size 
(PI. XX, fig. 2). One shown in the illustration of a sugar beet measured 
a full half-inch (PI. XXIII). They are usually much smaller, from i to 
3 mm., and those produced in cultures are likely to be quite irregular in 
outline. The sclerotia consist of interwoven branches, forming a loose 
pseudoparenchyma of uniform structure throughout. The sclerotia! 
hyphse are broken up into short cells each of which may function as a 
spore when placed under favorable conditions for development. The 
Corticium stage has not been observed upon the sugar beet, but the 
fungus appears to be identical with the form on the potato and a variety 
of other plants upon which the Corticium is common, and the name 
"Corticium vagum B. and C, var. solani Burt.," which is the one most 
generally accepted in America, is being retained for the purposes of this 
paper. 

The beet diseases produced by this fungus in America are imknown in 
Europe, and this fact has been used as an argument that they can not 
be correctly attributed here to the fungus which produces the sclerotia 
on potatoes there. This argument is fully met, however, when we 
approach a study of the environmental factors upon which the fungus is 
dependent for the production of disease, since the climatic and soil 
factors under which it becomes an active parasite in some portions of 
America are not found in Europe. 

INOCULATION EXPERIMENTS ON BEET SEEDLINGS 

The 34 cultures used in the inoculation experiments on seedlings were 
obtained from the following sources : 

Sugar-beet seedlings grown in the field at Rocky Ford, Colo., 5; at 
Madison, Wis., in Rocky Ford soil, 5; at Madison in Garden City, Kans., 
soil, 2 ; at Washington in greenhouse soil, 3 ; in sterilized soil infected 
with decayed beets, 2 ; in Madison greenhouse soil, i ; at Madison in 



154 Journal of Agricultural Research voi. iv. no. » 

field soil, i; crown-rot sugar beets from Rocky Ford, Colo., 5; from 
Garden City, Kans., 2; from Chino, Cal., i; from Kenosha, Wis., i; 
potato tuber from Carbondale, Colo., 1 ; radish from Madison, i ; carrot 
from Madison, i ; pine seedlings grown at Garden City (contributed by 
Mr. Carl Hartley, of the Bureau of Plant Industry), 2; and decaying 
tomato grown on Potomac Flats, Washington, D. C. (contributed by 
Dr. H. W. Wollenweber (44), of the Bureau of Plant Industry, as R. 
potomacensis Wollenw.), i. 

The various strains in cultures exhibited no striking dififerences. Those 
which did appear are due largely to difference in vigor. The virulence 
is reduced temporarily by long continuance in artificial culture. Differ- 
ence in the virulence of the several strains, both when freshly isolated and 
when rejuvenated, was sometimes noted, and this difference appeared to 
be quite constant, although it bore no relation to the host which furnished 
the original culture. For example, one of the two strains most virulent 
to beet seedlings was secured from the beet root and the other was the 
form from tomatoes received as R. potomacensis Wollenw. Certain of the 
strains that were least virulent were obtained originally from sugar-beet 
seedlings. 

The inoculations were carried out with extreme care, following the meth- 
ods already described. Every precaution was taken to insure the accuracy 
of the results, which were uniformly positive. Each strain was recovered 
and reinoculated into seedlings through from four to six generations. 

The type of disease produced upon beet seedlings is similar to that 
caused by Phoma beiae, but the plants are attacked at a younger stage, 
and the progress of decay is likely to be more rapid, so that it was neces- 
sary to exercise considerable care in making inoculations at the time of 
seeding. In the cases of heavy inoculation few or no seedlings broke 
through the soil. With lighter inoculation a milder form of damping-oS 
developed, or the disease took the form of root sickness, in which case a 
relatively large number of plants eventually recovered. The fungus is 
capable of attacking its host at any time after germination. Inoculations 
upon older seedlings also gave positive results. Young beets 4 or 5 weeks 
old were readily killed by inoculations upon the crown when no wound 
was made. 

DISTRIBUTION OF THE FUNGUS 

The distribution of the fungus is \e.vy general, but under field condi- 
tions damping-off due to Rhizoctonia is far more general in the soils of 
the semiarid West. Soils brought from western Kansas and Colorado to 
Wisconsin and placed in pots in the pathological garden yielded a large 
percentage of damping-off from Rhizoctonia sp. , while Wisconsin soils in 
control pots were practically free from the ravages of this parasite. The 
fungus has been isolated a few times from the Wisconsin beet fields, but 
it appears to be of little consequence as a beet parasite under Wisconsin 
conditions. The reverse is true in Colorado and Kansas, where a majority 



May IS. 191S Seedling Diseases of Sugar Beets 155 

of the diseased seedlings examined have yielded cultures of Rhizoctonia. 
The fungus is the cause of a very destructive crown-rot in the West 
(PI. XX, XXI, and XXII), where it frequently becomes epidemic. It is 
not uncommon to see entire fields of 50 or 100 acres practically destroyed 
in August by root-rot, of which there is no evidence earlier in the season 
(PI. XXI, fig. i). This form of rot is seen only occasionally in the more 
eastern beet-growing districts, where it appears to be of no economic 
importance. 

CONDITIONS INFLUENCING INFECTION 

The controlling influences in the distribution of the Rhizoctonia dis- 
eases of the beet may conceivably be associated with the unequal dis- 
tribution of the fungus or with differences in climate or in soil, or with 
any combination of these. Some light has been shed upon this point 
in the course of the inoculation experiments on growing beets. Field 
inoculations were first made in Wisconsin, using cultures obtained from 
Colorado and Kansas. The first series was made on August 21, 1912, 
by placing portions of mycelium upon agar among the heart leaves of 
beets in the field. The inoculations were made just at dark, and the beet 
leaves were moistened with water from a sprinkler, in imitation of a 
heavy dew. The morning of the 2 2d was cloudy, and a very little rain 
fell. The weather of the next few days was dry and hot. Examination 
a few days later showed that infection had occurred in all except one of 
the 29 beets inoculated. The disease, however, failed to make the 
progress typical of western conditions. At the time of harvest, October 
23, one beet showed no evidence of infection even at the point where 
inoculation was made and where the original dried culture was clearly 
seen. Six showed no injury other than slight lesions on petioles such 
as shown in Plate XXI, figure 2. Five showed old lesions on the crown, 
but they had entirely recovered. Eleven beets showed so slight evidence 
of decay that it was observed only on close examination. Five showed 
clearly defined decayed spots, but even these were restricted in area. 
One had entirely lost its original crown of leaves, but had formed scar 
tissue and had developed new leaves from the meristem at the sides. 
(PI. XXII, fig. I .) This was the only beet which had been injured for the 
commercial market, unless it might be that the sugar content of the 
others had been lowered. 

A second set of inoculations were made on August 28. In this 
instance 40 beets were inoculated by placing on the crown of each a 
portion of Rhizoctonia mycelium growing on a sterilized beet block. 
The results were very much like those of the first series. While the inoc- 
ulations took in every case, most of the beets outgrew the infection. 
Five beets were sufficiently injured to be unfit for market, but only one 
was killed. In these cases of serious infection the progress of the dis- 
ease corresponds closely to that seen in the West, although it was far 



156 Journal oj Agricultural Research voi. iv, no. 2 

less rapid. The fungus was readily recovered in culture from them. 
A photograph of the most seriously injured beet taken at the time of 
harvest on October 23 is reproduced in Plate XXII, figure 2. At that 
time the scars where the original infection had been produced could be 
found on all the beets. Some showed small areas of decay, but most 
of them were practically sound. 

A third series of inoculations were made on September 1 1 through knife 
wounds near the surface of the ground. These were made in imitation of 
cultivator injury and were infected by placing a rapidly growing culture 
of Rhizoctonia, sp. on a beet block directly in contact with the injured 
surface. Thirty beets were inoculated; none of them was destroyed. 
About half of the number healed completely, so as to leave only a local 
scar at the point of inoculation. The others showed local decay, more 
or less characteristic of crown-rot. The fungus was readily recovered 
from several of these. The largest decayed area produced was about 
4 inches in diameter. At least half of this beet was still sound. 

At the time of harvest the beets which showed no decay were topped 
to remove the leaves, the crown being left uninjured. They were placed 
on racks in the vegetable cellar and examined for decay from time to time. 
On April 3 all but two of them showed evidence of rot, although in most 
cases a close examination was necessary to discover it. Eighteen were 
selected and submitted to cultural tests for Rhizoctonia. Out of 68 
attempts to isolate the organism 54 yielded Phoma heiae, 1 failed 
to develop, and the remaining 12 gave growths of various saprophytes. 
In no instance was it possible to secure a culture of Rhizoctonia. It was 
apparent that those beets which failed to develop decay in the fields had 
entirely thrown off the infection from Rhizoctonia. 

In order to determine to what extent this resistance to attack is to be 
attributed to local conditions of climate or soil, two large lots of soil from 
seriously infected beet fields, one in Kansas and one in Colorado, were 
shipped to Madison, Wis. Both types of soil were quite heavily infected 
with Rhizoctonia sp. That from Kansas was a sandy loam deficient in 
organic matter. It had received generous applications of factory waste 
lime and was of good mechanical texture. The Colorado soil was of 
compact structure containing an admixture of clay and fine silt. It was 
very deficient in organic matter, so that it was quite impervious and 
lumped badly. These soils were placed in unperforated, unglazed, 
12-inch crocks containing cinders at the bottom for drainage, and sunk 
into the ground out of doors to within 2 inches of the top. Soil from 
Madison was employed in similar crocks as a control. Six crocks of 
each soil were sterilized in an autoclave by heating for 12 consecutive 
hours under 15 pounds' pressure, and six were left untreated. Untreated 
beet seed which showed remarkably strong germination and less than 
I per cent of infection with Phoma hctae was sown. Damping-off developed 
only in the unsterilized soil from Kansas and Colorado. Attempts to 



May 15, 191S 



Seedling Diseases of Sugar Beets 



157 



isolate the causal organisms in 27 cases gave the following results: 
Rhizoctonia, 15; Phoma, 8; Fusarium, 2; Mucor, i; undetermined, i. 
Both of the parasitic forms were isolated from each of the two types of 
soil developing disease. A good stand, which was thinned to three, 
four, or, in a few cases, five plants per pot, was secured in each crock, 
however, in spite of damping-off. Early in July evidences of crown-rot 
developed in four of the six pots of unsterilized Colorado soil, but not in 
that from Kansas. In two of these pots the stand was entirely destroyed 
by July 21, and in a third there remained only one small seedling with 
four leaves, which appeared after the original stand had been killed. 
No disease appeared in the pots of sterilized soil, nor did root-rot develop 
in the unsterilized Kansas soil. On July 23 inoculations were made with 
a recently isolated Kansas strain of Rhizoctonia in two pots of each of the 
six classes of soils. Two pots of each class were reserved as controls, and 
two were inoculated with Phoma betae, as previously reported. The 
inoculations were made on one beet only in each pot, by placing a piece 
of beet-block culture on the crown and a second fragment against a 
wound just below the surface of the soil. The other beets in the pots 
were not disturbed in any way. One beet in each control pot was 
wounded in a manner similar to that employed in the inoculations. 

The results in inoculated and in uninoculated pots are given in Table 
V. It is worthy of note that as a result of inoculating i beet in each of 
12 pots, 26 beets were killed and 7 more were so seriously diseased as to 
be made worthless, while only 3 resisted infection. One beet attacked 
in July by spontaneous rot recovered later. The fungus was recovered 
in culture from several of the diseased roots. 



Table V. — Results of pot experiments with Rhizoctonia rot 

INOCULATED POTS 





Pot No. 


Number 
of beets 
in pot on 
Jnly 21. 


Condition on October iS. 


Source of soil. 


Number 
dead. 


Number 
infected 

but 
living. 


Number 
sound. 




19 

22 

I 

4 

25 
28 

31 

34 
13 
16 

7 
10 


3 
I 

4 
4 
3 
4 
? 

4 
2 

3 
3 
3 


3 

3 
2 
2 
2 

2 

4 
I 
I 
3 
3 






Do 


I 

2 

I 
I 






I 


Do 




Kansas > 

Do 


I 






Do 








I 
I 




Do 


I 


Wisconsin (sterilized) 




Do 












Total 


36 


26 


7 


3 







^ The original stand of three beets had already been destroyed by spontaneous Rhizoctonia rot. 
one plant living resulted from seed delayed in germination. 



The 



158 



Journal of Agricultural Research 



Vol. IV. No. > 



Table V. — Results of pot experiments with Rhizoctonia rot — Continued 

UNTNOCULATBD POTS 





Pot No. 


Number 
of beets 
in pot on 
July 31. 


Condition on October 18. 


Source of soil. 


Ntimber 
dead. 


Number 
infected 

but 
living. 


Nimiber 
sound. 


Colorado 


20 

23 
2 

5 
26 
29 
32 
35 
14 
17 

8 
II 










Do 


"5 

: 

3 
3 
2 

3 

4 
3 
3 
3 


I 




"5 
4 
5 
3 
3 


Colorado (sterilized) 


Do 






Katlsa.-? 






Do 






Kansas (sterilized) 






Do 






3 

4 

64 

3 
3 


Wisconsin 






Do 












Do 












Total 


37 


I 




39 







« Two of these beets were diseased with Rhizoctonia rot. One of them eventually recovered, and the 
other died. 
& The additional beet is Icnown to have resulted from seed delayed in germination. 

Other inoculations with Rhizoctonia were made on beets growing in 
the field at Madison, Wis., Garden City, Kans., and Rocky Ford, Colo. 

Of 30 plants inoculated at Madison on July 23, i escaped infection, 2 
were infected but recovered, and 27 were killed. The fungus was re- 
covered in culture from several of them. The control plants, of which 
there were several hundred, remained healthy. 

The inoculations at Garden City were made on July 27 on beets fur- 
nished by Dr. C. F. Clark, of the Bureau of Plant Industry, who kindly 
made the field observations. The field was known to be somewhat 
infected with Rhizoctonia. One row was inoculated, those adjacent on 
either side being reserved as controls. The same procedure was observed 
in the inoculations with Phoma betae, previously reported, but since these 
did not produce disease, five rows, or 150 beets, became available for 
controls. Of the 30 inoculated plants, 23 were killed, 2 others were 
so seriously injured at the crown as to become entirely defoliated and 
apparently dead but developed a few new leaves late in the fall (October), 
and 5 escaped infection. The rate of progress of the disease is shown in 
Table VI. Three control beets became infected during the season. 



Uay 15, 1915 



Seedling Diseases of Siigar Beets 



159 



Table VI. — Results of inoculation experiments with Rhizoctoniasp. at Garden City, Kans. 





Treatment. 


Number of dead sugar-beet plants on — 


Total 
number 
of dead 
plants. 


Number 
of 


Row 

No. 


Aug. 

7. 


Aug. 
13. 


Aug. 
33. 


Sept. 
3- 


Sept. 
17. 


Sept. 
23. 


healthy 

plants 

on Sept. 

23. 


1 


Control 




2 

I 






I 






I 
II 







6 







I 








4 
I 





I 
"25 
I 
I 




29 

5 
29 
29 
30 
30 


2 
3 
4 
5 
6 


Rhizoctonia 

Control 


Do 

Phoma betae 

Control 







» Two of these made feeble effort at recovery in October, showing that a Uttle parenchyma had survived. 

The 30 beets inoculated at Rocky Ford were killed, while all the con- 
trols remained healthy (PL XX, fig. i). 

A consideration of the facts related indicates that soil properties are 
potent factors influencing the susceptibility of beets to attack by Rhi- 
zoctonia. It has long been maintained that clay soils and those which 
are seriously deficient in organic matter and of fine, compact texture, 
so as to bake readily, are most likely to develop Rhizoctonia diseases. 
Further indication of this is found in the development of spontaneous 
root-rot in the Colorado soils used in the pot experiments at Wisconsin. 
It did not develop in the other soils employed, although the amount of 
Rhizoctonia damping-off indicated that the Kansas soil was at least as 
heavily infected with Rhizoctonia as was the Colorado material. The 
experimental data lead to the conclusion, however, that, in the case of 
the Rhizoctonia root-rot of the beet, soil temperature is a more im- 
portant factor than soil texture. The inoculations in the field at Madi- 
son in 1912 were made at the beginning of a very hot period which en- 
dured for several days. Infection was produced uniformly, but in 
practically every case the beets completely recovered during the cooler 
weather which set in a few days after the inoculations were made. In 
1913 infection was attempted at an earlier date when it might be ex- 
pected that a somewhat longer period of hot weather would ensue. This 
proved to be the case and, as already pointed out, the inoculations were 
very generally successful. It is also significant that the cases of partial 
or complete recovery which occur appear late in the season when the soil 
temperatures are considerably lowered. 

PYTHIUM DEBARYANUM 

Hesse (24) reported Pythiuvi deharyanum Hesse as a damping-ofif 
parasite of beets in 1874, but his experimental work appears to have 
been done on other hosts, so that while no one has doubted the accuracy 
of Hesse's deductions, Peters (33, p. 221) appears to have been the first 
to demonstrate by culture methods that this fungus includes the sugar 
90271°— 15 5 



i6o Journal of Agricultural Research voi. iv, No. 2 

beet among its hosts. The fungus is so well known that a description 
here is superfluous. It is very readily secured in pure culture and is 
easily carried upon media (PI. XVI, fig. i). It grows especially well with 
long-continued vitality upon string-bean agar. The sexual fruiting 
bodies are quite common in Petri-dish cultures upon this medium, but 
are rarely met with in tube cultures. The asexual conidia, as well as 
oospores, are formed abundantly when the fungus is grown in vt^ater 
upon sugar-beet seedlings in Petri dishes. The cultures obtained through- 
out the experiments were invariably identified by fruiting bodies, and 
the same method was applied in proving up the cultures recovered from 
artificial inoculation. Suspected seedlings were treated in bichlorid of 
mercury, rinsed in water, and plated upon the acid synthetic agar pre- 
viously mentioned (p. 137). When growth developed, the mycelium 
was examined through the bottom of the Petri dish by inverting the plate 
upon the stage of the microscope. If no septa were visible, the seedling 
was transferred to a sterile Petri dish after a subculture had been made 
from the growth. Sterile water was added to the fresh plate con- 
taining the seedling. In case the growth was Pythium debaryanum, 
the characteristic conidia developed in great numbers in from 24 to 48 
hours, to be followed during the next few days by oospores. Direct 
germination of conidia was often seen and could be very readily induced 
by adding a fresh beet seedling to the culture. Germination by zoo- 
spores was not observed, but no special effort was made to induce this 
type of development. 

The cultures used in the inoculation experiments were all morpholog- 
ically identical, so far as could be determined. They were secured from 
the following sources : 

Damped-off beets grown at Washington in the greenhouse, 2 ; at 
Madison, Wis., in the greenhouse, 6; at Madison in the greenhouse in 
Utah soil, 3 ; at Madison in the greenhouse in Michigan soil, 2 ; damped- 
off seedlings grown in Utah in the field, i ; grown in Wisconsin in the 
field, I ; grown in Colorado in the field, i ; damped-off pine seedlings from 
Kansas (contributed by Mr. Carl Hartley, of the iJureau of Plant Indus- 
try), I ; decaying potatoes, isolated in 1909, i. 

Mr. Hartley reported this strain pathogenic to pine seedlings, having 
produced damping-off with it to the extent of 100 per cent in the seed 
bed. 

Pythium debaryanum proved to be exceedingly destructive in the pot 
experiments. When infection was made at the time of seeding, even a 
temporary stand was seldom secured. Examination showed that the 
seed germinated, but that the plants were destroyed before they could 
come up. In many cases the embryo was killed while still within the 
seed. By delaying the inoculation until the seedlings were well started 
typical damping-off was produced and the fungus recovered. It was a 
very common thing to find infection on the tips of the cotyledons. 



May IS. 191S Seedling Diseases of Sugar Beets 161 

This probably occurred while the leaves were still within the seed coat. 
The fungus was found to be capable of attacking the beet after it was 
5 or 6 weeks old. Peters's statement (33, p. 228) that it is able to infect 
the side roots during the entire vegetative period is probably correct. 
When the taproot is once attacked by P. debar yanum, the ultimate 
death of the plant seems to be assured. Fortunately the soil relations 
in early seeding time are usually not sufficiently favorable to the rapid 
development of the fungus to make it an aggressive parasite under 
average field conditions. This fungus does not develop well in cold 
soil, but does its most serious work under seed-bed and greenhouse 
conditions or in the fields which have been seeded very late when the 
soil temperatures have begun to rise. 

UNDESCRIBED SPECIES INJURIOUS TO SUGAR BEETS 

In the author's preliminary note (12) it was reported that Aphanomyces 
laevis De By. had been found as a damping-ofF fungus of sugar beets in 
America, but subsequent detailed morphological studies of the fungus 
as it developed in artificial culture and on beet seedlings have shown 
that it differs in some important respects from the published descriptions 
of De Bary and others. A . laevis was first reported in a parasitic relation 
by Peters (31) in 1906. He found the fungus as a damping-off parasite of 
considerable importance upon sugar beets in Germany. Barrett (4) has 
reported its occurrence in America as the cause of a disease of radishes. 
The first cultures of the fungus temporarily mistaken for A. laevis 
were secured from damped-off beet seedlings grown in soil which had pre- 
viously produced the black-root disease of the radish, like those shown 
in Plate XXIV, figure 2. It was later obtained from soils at Madison, 
and from Kenosha, Wis., as well as from seedlings damping-off in soil 
which had been infected with fragments of a diseased radish obtained 
from Illinois. The causal relation of the organism to the radish disease 
as well as to damping-off of sugar-beet seedlings was confirmed repeatedly 
by inoculation experiments, and it was at first thought possible that the 
discrepancies between this fungus and published descriptions of .4 . laevis 
might be the result of response to the changed environmental conditions 
of culture or to variations within the species, since it is well known from 
the study of many investigators that the Saprolegniaceae are exceedingly 
variable. Through the courtesy of the Kaiserliche Biologische Anstalt 
at Dahlem, Germany, and Dr. Leo Peters, of that institution, the author 
was permitted to isolate Aphanomyces from the experimental fields of 
the Anstalt. An organism was secured from damped-off seedlings, which 
Dr. Peters identified as the organism with which he had worked and which 
conformed in every respect to De Bary's description of A . laevis. It was 
secured in pure culture, and its pathogenicity to beet seedlings was con- 
firmed by inoculation experiments. Unfortunately the culture was lost 



1 62 Journal of Agricultural Research voi. iv. no. a 

before it had been tested upon the radish and thereafter could not be 
secured again. The morphological studies, however, prove that the 
American fungus with which we have been working is not A . laevis, but 
a hitherto undescribed organism. Morphological, physiological, and 
cytological studies will be presented in another paper. 

In the work with sugar-beet seedlings five strains of the organism were 
employed which were obtained from the following sources: 

Seedling sugar beets grown at Madison, Wis., 2; at Kenosha, Wis., i; 
in soil originally infected by radishes showing black-root, 2. 

The disease which it produces on the sugar beet is very similar to that 
caused by Pythium deharyanum. The fungus is even more aggressive as 
a parasite than Pythium (PI. XXIV, fig. i). When the inoculations were 
made at the time of seeding, it was unusual for plants to appear above- 
ground. The evidence obtained all goes to show that a seedling once 
attacked never recovers. 

A disease of the side roots of growing beets was encountered during the 
course of the studies in soils which had been inoculated with artificial 
cultures of the fungus several months earlier. A photograph of a speci- 
men is reproduced in Plate XXIII, figure 2. The fungus was readily iso- 
lated from diseased side roots of this beet and there appears to be no 
reason to doubt its causal relation to the trouble. Peters (33, p. 244) 
has quoted a similar disease of European beets caused by Aphanomyces. 

Comparatively little is known regarding the range of distribution of 
the fungus. What appears to be the black-root of radish has been 
observed in the District of Columbia, Marj'land, Virginia, Long Island, 
Illinois, and at several points in Wisconsin, and there is reason to believe 
that other workers have found it in various places, although no records 
of such observations have been published. The disease produced by this 
fungus is so similar to that reported by Barrett (4) that they are not 
readily distinguishable, and it may be that either of these organisms is 
responsible for the disease in any of the stations mentioned. The author 
does not consider that his results should be construed to throw doubt 
upon the accuracy of Barrett's observations, merely wishing to record 
a radish disease that is indistinguishable in external appearance from 
that produced by Aplianomyces laevis, but which is due to this hitherto 
undescribed parasite. 

The fungus is readily isolated from beet seedlings by the method al- 
ready described for Pythium deharyanum. In this case, however, the 
subcultures should be made to string-bean agar, upon which the organ- 
ism produces a luxuriant growth. Sterilized beet seedlings in water in 
test tubes make an excellent medium for the cultivation of this fungus. 
The limit of vitality in culture has not been determined, but transfers 
made to string-bean agar on July 2 from beet-seedling water cultures 
made on February 12 developed a heavy growth overnight, showing 
not the least loss of vitality. 



May 15, 191S Seedling Diseases of Sugar Beets 1 63 

The vegetative stage of the fungus is strikingly like that of P. debary- 
anum, so that they can not be distinguished readily except by the fruit- 
ing bodies, which develop readily in water cultures in plates in from 24 
to 48 hours. The zoospores develop first, to be followed somewhat 
later by the Pythium-like oospores. The asexual fruiting bodies are 
first noted as the swollen ends of hyphae, which vary greatly in length and 
are characteristically somewhat branched. They average from 150 to 
goofi in length or even more. When mature, these bodies discharge 
their contents in a spherical mass which cleaves in the course of 20 or 
30 minutes, giving rise to numerous zoospores. 

OTHER FUNGI FOUND ON SUGAR BEETS 

In the course of the isolation work various other fungi were secured. 
Some of these were known saprophytes, while others, like Macrosporium, 
Mucor, and Botrytis, have sometimes been reported in parasitic rela- 
tions, but gave negative results in our trials. Fusarium and Verticillium 
cultures were secured frequently, but inoculation experiments with these 
genera were deferred pending the completion of taxonomic work by 
other investigators. 

There remains to be discussed a peculiar type of decay of growing 
beets and a root sickness of seedlings associated with Rhizopus nigricans 
Ehr. Cultures of this fungus were frequently isolated in the course of 
experimental work from seedlings. Specimens of mature beets affected 
by a peculiar light-brown decay were received in the laboratory from 
California during the campaign of 1910. The interior portion of these 
beets yielded a very large proportion of cultures of Rhizopus. The 
decay was very characteristic and unlike anything before seen. In the 
early stages the material was almost normal in appearance, except for 
the discoloration. It later assumed a somewhat flabby texture and 
developed pockets in the interior which were filled with a nearly colorless 
fluid rich in acetic acid, as was determined by the odor and by chemical 
tests. 

In 1 91 2 a somewhat similar trouble was reported from Colorado, and 
a visit was made to the field (PI. XXV, fig. i ) . The beets at that time were 
dead over considerable areas. Those most recently attacked showed the 
same light-brown color previously referred to (PI. XXV, fig. 2), while those 
in the more advanced stages of decay presented various symptoms be- 
tween the early condition and almost complete dissolution of all except 
the vascular tissue. Some, however, were apparently pickled in acetic 
acid, formed probably from the fermentation of the carbohydrate con- 
tent. A very large number of attempts to isolate an organism of known 
pathogenic properties was made. The trials yielded Rhizopus nigricans 
in pure cultures to the extent of almost 100 per cent. Inoculation work 
in the laboratory upon dormant beets in moist chambers resulted in the 



164 Journal of AgriciiUural Research voi. iv. No. 2 

reproduction of decay similar in appearance to that occurring in the two 
cases described. The acetic-acid development, however, did not occur 
except in a slight degree in a few instances, and there is no certainty 
that in these cases it did not result from contamination. Inoculation 
experiments made in the field upon living material invariably yielded 
negative results. Inoculation experiments upon seedlings made in the 
usual manner also failed to produce damping-ofl when reasonably good 
conditions of culture were maintained. It was possible, however, to 
produce a disease which showed the symptoms of root sickness when 
the soil was excessively wet and the temperature rather adverse. Nat- 
urally the fungus was easily isolated from such material. The control 
plants, however, were sickly or diseased on the roots, and it is highly 
probable that the results obtained in the inoculation experiments with 
seedlings are to be attributed to physiological injury, which opened the 
way for the Rhizopus to grow saprophytically upon the tissue. 

Inquiry into the history of the fields that produced the peculiar rot 
with which this fungus was associated revealed the fact that at least 
one of them had been flooded for a time and that the other had been 
excessively moist for several consecutive days prior to the appearance of 
the disease. In view of these facts and the results of experimental work, 
it seems reasonable to conclude that the beets were originally killed or 
at least materially weakened by adverse physiological conditions and 
that Rhizopus nigricans followed as a saprophyte or weakling parasite 
producing a characteristic type of decay. 

ALKALI INJURY TO SUGAR BEETS 

During a field trip in Colorado late in August, 191 2, the writer was 
called upon to visit a beet field in which a peculiar rot was developing. 
The beets had made a good growth, and most of them were above the 
average in size. The foliage was luxuriant, but was characterized by a 
bluish green color and a brittle texture. Little evidence of disease, 
aside from the abnormal appearance of the foliage, was evident until 
the plants were pulled, when it was seen that many beets were decayed 
at the lower portion of the root. Some agency had killed the taproot, 
following which a soft rot was destroying the tissue. A majority of the 
plants in the portions of the field most seriously affected showed a 
characteristic cracking- and corroding of the root, like that shown in 
Plate XXVI. 

Evidences of alkali could be seen on the surface of the soil here and 
there, and it seemed probable that the deeper branches of the taproot had 
been killed by alkaline waters. This probability was increased by the 
fact of the close proximity to the field of an irrigation reservoir the waters 
of which were evidently quite alkaline, as could be seen from the crust of 
salts on the ground at the edge of the lake. As a further test upon this 
opinion, several beets were taken to the laboratory and attempts were 



May 15. 191 5 Seedling Diseases of Sugar Beets 165 

made to isolate pathogenic organisms, but with negative results. Several 
of the plants upon which decay already had made considerable progress 
were placed in fresh soil in the greenhouse and held under observation to 
determihe whether the disease would continue to develop. Without ex- 
ception these plants healed and thereafter showed no evidences of disease. 
The foliage which they put forth was normal, giving no evidence of the 
brittleness or blue-green color noted in the field. The results seemed to 
justify the conclusion that the plants were suffering from excessive alkali 
brought in by seepage from the neighboring reservoir. 

SUMMARY 

The more important points brought out in this paper may be sum- 
marized as follows : Four fungi have been found to stand in a causal rela- 
tion to damping-off of sugar beets in America. These are Phoma betae 
(Oud.) Fr. ; Rhizoctonia sp. probably identical with Corticium vagwm B. and 
C, var. solani Burt.; Pythium debaryanum Hesse; and an undescribed 
member of the Saprolegneaceae. 

Under favorable conditions of culture, plants attacked by Phoma betae 
or Rhizoctonia may recover either temporarily or permanently. Attacks 
of the other two fungi upon the seedlings may be expected to prove fatal. 
Phoma and Rhizoctonia are capable of producing characteristic decay in 
mature beets. The former appears to infect the plants primarily in the 
seedling stage, and when recovery occurs it remains thereafter in a dor- 
mant condition upon the host. It occasionally develops a characteristic 
black rot on growing beets in the field and more frequently appears upon 
mother beets in storage. When it does not destroy the root, it may infect 
the seed stalk and appear upon the mature seed. Control measures are 
to be sought in proper cultural methods and seed treatment which looks 
forward to the production of seed free from infection. Pythium debary- 
anum is capable of attacking the feeding roots of the beet throughout its 
vegetative period, and the new fungus is also able to cause trouble on 
mature beets in a similar manner. Rhizopus nigricans Ehr., while unable 
to produce disease on normal plants in the field, is capable of attacking 
the tissue of dead or dormant sugar beets, producing a characteristic 
decay. 

LITERATURE CITED 

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(3) 

1907. Physiology of a simple parasite. Pt. 2. In Yearbook, Khediv. Agr. 
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1912. A serious root disease of radish. (Abstract.) In Phytopathology, v. 2, 
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1 66 Journal of Agricultural Research voi. iv.no. a 

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19 13. Damping-off and root rot parasites of sugar beets. In Phytopathology, 
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(13) EiDAM, Eduard. 

1888. Untersuchungen zweier Krankheits-Erscheinungen die an den Wurzeln 
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(15) 

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(17) 
(18) 

(19) 
(20) 



1894. Zur Bekampfung von Phoma Betae. In Ztschr. Ver. Riibenz. Indus. 
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1895. Neue Untersuchungen iiber Phoma Betae. In Ztschr. Ver. Riibenz. 
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1896. Bericht iiber Versuche zur Bekampfung der Herz und Trockenfaule der 
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May IS. 191S 



Seedling Diseases of Sugar Beets 167 



(21) Gtrssow, H. T. . c- t^ t ^ aa 

1905. Potato scurf and potato scab. In Jour. Roy. Agr. Soc. England, v. 66, 

P- 175- 

(22) Hedgcock, G. G. , t, * r 

1904. Proof of the identity of Phoma and Phyllosticta on the sugar beet. In 
Jour. Mycol., v. 10, no. 69, p. 2-3. 

(23) HSLLRIEGEL, F. H. „..i. . ,,„, 1 

1890 Welche Bedeutung hat die Schadigung der jungen Ruben durch Wurzel- 
brand (schwarze Seine) und welche Mittel gegen dies Uebel sind 
bekannt? In Deut. Zuckerindus., Jahrg. 15, No. 24, p. 745- 

(24) Hesse, Rudolph. ■ , r^ u 

1874 Pythium de Baryanum ein endophytischer Schmarotzer m den Geweben 
der Keimlinge der Leindotter, der Ruben, des Spergels und emiger 
anderer landwirtschaftlichen Kulturpflanzen. 76 p., 2 pi. Halle 
a/S. Inaugural-Dissertation— Gottingen. 

(25) KrugER, Friedrich. ,u a a -d u „ 

1803 Phoma Betae (Frank), als einer der Erreger von Wurzelbrand der Ruben- 
pflanze. In Ztschr. Ver. Riibenz. Indus. Deut. Reichs, Bd. 43 ("• F. 
Jahrg. 30), p. 730-743- 

1893 Weitere Untersuchungen iiber die neue Krankheit der Zuckerrube 
verursacht durch Phoma Betae (Frank). In Ztschr. Ver. Riibenz. 
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(27) KUHN, J. G. 

1858. Die Krankheiten der Kulturgewachse ... 312 p., 7 pi. iserim. 

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illus., 9 pi. Copenhagen. 

(29) OUDEMANS, C. A. J. A. r ,■ n . .. T f 

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1876. In Nederland. Kruidk. Arch., s. 2, deel 2, stuk 3, p. 176-188. 

(10) Pammel, L. H. , , a d 

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Forstw., Bd. 8, Heft 2, p. 211-259, 12 fig. 

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191 5. Phoma betae on the leaves of the sugar beet. In Jour. Agr. Research, 
V. 4, no. 2, p. 169-178. 

(35) PrilliEux, E. E. . „ ,, , c 

1891. La pourriture du coeur de la betterave. In Bui. Soc. Mycol. France, 

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(36) • 

1895-1897. Maladies des Plantes Agricoles ... 2 t. Paris. 

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1891 . Complement a 1 'etude de la maladie du coeur de la betterave . In Bui. 
Soc. Mycol. France, t. 7, p. 23-25, pi. 3. 



1 68 Journal of Agricultural Research voi. iv.no. a 

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(39) 

1904. Potato failures. A second report. Colo. Agr. Exp. Sta. Bui. gi, t,^ p., 

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PLATE XVI 
Isolation cultures from sugar-beet seedlings. 



Fig. I. — Rhizoctonia sx>. 

Fig. 2. — Pythium debaryanum. 



Seedling Diseases of Sugar Beets 



Plate XVI 





Journal of Agricultural Research 



Vol. IV, No. 2 



Seedling Diseases of Sugar Beets 



Plate XVII 





Journal of Agricultural Research 



Vol. IV, No. 2 



PLATE XVII 
Phoma betae. 

Fig. I. — Isolation culture from sugar-beet seedling. 
Fig. 2. — Fruiting culture on string-bean agar. 



PLATE XVIII 

Fig. I. — Half -grown sugar beets showing crown-rot caused by Phoma beiae. 
Fig. 2. — Sugar beet showing seedling injury caused by Phoma hetae. 



Seedling Diseases of Sugar Beets 



Plate XVIII 





Journal of Agricultural Research 



Vol. IV, No. 2 



Seedling Diseases of Sugar Beets 



Plate XIX 




Journal of Agricultural Research 



Vul. IV, r^o. 2 



PLATE XIX 
Mother beet showing storage decay caused by Phoma betae. 



PLATE XX 

Rhizoctonia sp. : Root-rot of sugar beet. 

Fig. I. — Result of artificial inoculation, control beet in center. 

Fig. 2. — Result of natural field infection. Note sclerotia on specimens at right. 



Seedling Diseases of Sugar Beets 



Plate XX 





Journal of Agricultural Research 



Vol. IV, No. 2 



Seedling Diseases of Sugar Beets 



Plate XXI 





Journal of Agricultural Research 



Vol. IV, No. 2 



PLATE XXr 

Fig. 1.— Sugar beet showing field-rot caused by Rhizodonia sp. Natural infection. 
Fig. 2.— Sugar beet showing artificial infection with Rhizodonia sp. on the petiole. 
The disease has been arrested. 



PLATE XXII 

Results of artificial inoculation with Rhhocionia sp. 

Fig. I.— Sugar beet, photographed from above, showing original crown destroyed, 
and new leaves developing from the sides. 

Fig. 2. — Section of sugar beet showing character of Rhizoctonia injiuy. 



Seedling Diseases of Sugar Beets 



Plate XXII 





Journal of Agricultural Research 



Vol. IV, No. 2 



Seedling Diseases of Sugar Beets 



Plate XXIl 




Journal of Afjricultural Research 



Vol, IV, No. 2 



PLATE XXIII 

Fig. I. — Sugar beet showing large sclerotium {yi inch) resulting from artificial inocu- 
lation with Rhizoctonia. The beet has resisted infection. 

Fig. 2. — Half -grown sugar beet showing injury to feeding roots due to an undescribed 
parasite. 

90271°— 15 6 



PLATE XXIV 

Fig. I. — Sugar beet showing dampingoff due to an undescribed parasite; control 
pot at right. 

Fig. 2. — Radish showing black-root caused by the same fungus. 



Seedling Diseases of Sugar Beets 



Plate XXIV 





Journal of Agricultural Research 



Vol. IV, No. 2 



Seedlincr Diseases of Supar Beets 



Plate XXV 





Journal of Agricultural Research 



Vul. IV, No. 2 



I 



PLATE XXV 



,.- r Field in which Rhizopus rot developed. 

vl ..-Ty^cal beets from the field shown « figure x. 



PLATE XXVI 
Sugar beet showing alkali injury. 



Seedling Dist'a^es of Sugar Beets 



Plate XXVI 




Journal of Agricultural Research 



Vcl. IV, No. 2 



LIBRARY OF CONGRESS 



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